Cambrian Stage 10
Stage 10 of the Cambrian is the still unnamed third and final stage of the Furongian Series. It follows the Jiangshanian and precedes the Ordovician Tremadocian Stage. The proposed lower boundary is the first appearance of the trilobite Lotagnostus americanus around 489.5 million years ago, but other fossils are also being discussed (see below). The upper boundary is defined as the appearance of the conodont Iapetognathus fluctivagus which marks the beginning of the Tremadocian and is radiometrically dated as 485.4 million years ago.
The 10th stage of the Cambrian has not been formally named by the ICS yet, although a number of local names exist. Several authors favor the name "Lawsonian" after Lawson Cove, in the Wah Wah Mountains of Utah.
The ICS is still discussing which geological section and biostratigraphic marker will be used to define the base of the 10th Cambrian stage.
Likely candidates for the section are still investigated. A first proposal was a section near Duibian, Zhejiang province (China). Newer publications favor Steamboat Pass in the House Range of Utah. If a conodont is used for the base the stage then many more sections would be likely candidates for the GSSP, e.g. in Australia, Kazakhstan and Canada.
Candidates for the biostratigraphic marker are the first appearance of a trilobite or conodont species. The trilobite Lotagnostus americanus was first suggested by the ICS, but has proven to be problematic. In 2006 another working group proposed the first appearance of Cordylodus andresi. Currently the first appearance of Eoconodontus notchpeakensis is favored by many authors because it is globally widespread and is independent of facies (known from continental rise to peritidal environments).
The Eoconodontus notchpeakensis proposal would also incorporate a non-biostratigraphic marker to correlate the beginning of Stage 10 globally. A carbon isotope excursion (the HERB-event) occurs in the lower part of the E. notchpeakensis range.
Cambrian Stage 10 can be subdivided using different biostratigraphic zones. Several conodont zone and subzones can be distinguished. The same is true for trilobites.
- "Stratigraphic Chart". International Commission on Stratigraphy. Retrieved 17 November 2012.
- "GSSP Table - Paleozoic Era". Geologic Timescale Foundation. Retrieved 17 November 2012.
- Landing, E.; Westrop, S.R.; Adrain, J.M. (19 September 2011). "The Lawsonian Stage - the Eoconodontus notchpeakensis FAD and HERB carbon isotope excursion define a globally correlatable terminal Cambrian stage". Bulletin of Geosciences: 621–640. doi:10.3140/bull.geosci.1251.
- Miller, J.F.; Evans, K.R.; Freeman, R.L.; Ripperdan, R.L.; Taylor, J.F. (4 August 2011). "Proposed stratotype for the base of the Lawsonian Stage (Cambrian Stage 10) at the First Appearance Datum of Eoconodontus notchpeakensis (Miller) in the House Range, Utah, USA". Bulletin of Geosciences: 595–620. doi:10.3140/bull.geosci.1255.
- Miller, James F.; Ethington, Raymond L.; Evans, Kevin R.; Holmer, Lars E.; Loch, James D.; Popov, Leonid E.; Repetski, John E.; Ripperdan, Robert L.; Taylor, John F. (31 July 2006). "Proposed stratotype for the base of the highest Cambrian stage at the first appearance datum of Cordylodus andresi, Lawson Cove section, Utah, USA". Palaeoworld. 15 (3-4): 384–405. doi:10.1016/j.palwor.2006.10.017.